U.S. patent number 4,733,355 [Application Number 06/828,155] was granted by the patent office on 1988-03-22 for non-contacting range sensing and control device.
This patent grant is currently assigned to Agtek Development Company, Inc.. Invention is credited to Richard W. Davidson, John W. Fletcher.
United States Patent |
4,733,355 |
Davidson , et al. |
March 22, 1988 |
Non-contacting range sensing and control device
Abstract
A non-contacting range sensing and control device for
controlling the position of a grading implement relative to a datum
is disclosed. The device includes a non-contacting distance
measuring device that periodically measures the separation distance
between the distance measuring device and the datum. Also included
is a reference circuit that defines consecutive first, second, and
third intervals for comparison to the separation distance, and a
comparison circuit that periodically compares the intervals to the
separation distance, and generates a positive error signal if the
separation distance is within the limits of the first interval,
generates no error signal if the separation distance is within the
limits of the second interval, and generates a negative error
signal if the separation distance is within the limits of the third
interval.
Inventors: |
Davidson; Richard W. (Dublin,
CA), Fletcher; John W. (Pleasanton, CA) |
Assignee: |
Agtek Development Company, Inc.
(Livermore, CA)
|
Family
ID: |
25251044 |
Appl.
No.: |
06/828,155 |
Filed: |
February 10, 1986 |
Current U.S.
Class: |
701/50; 172/4;
172/4.5; 56/10.2R; 700/302 |
Current CPC
Class: |
G01S
15/18 (20130101); E02F 3/847 (20130101); E02F
3/842 (20130101); B60G 2300/09 (20130101); B60G
2401/176 (20130101) |
Current International
Class: |
E02F
3/76 (20060101); E02F 3/84 (20060101); G01S
15/18 (20060101); G01S 15/00 (20060101); A01D
075/28 () |
Field of
Search: |
;364/424,561,562
;56/10.2,DIG.15 ;377/16,17 ;73/624,629,640 ;172/4,4.5,26 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chin; Gary
Attorney, Agent or Firm: Limbach, Limbach & Sutton
Claims
What is claimed is:
1. An apparatus for controlling the position of a grading implement
of an earth-moving vehicle relative to a datum that extends along
the direction of travel of the vehicle and that is elevated above
ground level, said apparatus comprising:
position adjustment means coupled to the implement for moving the
implement in one direction relative to the datum in response to a
positive error signal and for moving the implement in an opposite
direction relative to the datum in response to a negative error
signal;
sonic means coupled for movement with the implement for
periodically transmitting a sonic signal downward toward the datum
and for receiving a sonic signal reflected upward from the datum,
wherein the time period between the transmission and receipt of
said sonic signal defines a measurement time period that is
proportional to the separation distance between said sonic means
and the datum;
timing means for periodically defining consecutive first, second,
and third comparison time intervals of finite duration, wherein
said first comparison time interval defines a positive error region
beginning at a time after the transmission of the sonic signal by
said sonic means, said second comparison time interval defines a
nominal error region beginning at the end of said first comparison
time interval, and said third comparison time interval defines a
negative error region beginning at the end of said second
comparison time interval; and
comparison means for periodically comparing said measurement time
period to said comparison time intervals, for generating said
positive error signal if said measurement time period ends during
said first coparison time interval, for generating said negative
error signal if said measurement time period ends during said third
comparison time interval, for generating no error signals if said
measurement time period ends during said second comparison time
interval, for generating no error signals if said measurement time
period ends before said first comparison time interval begins, and
for generating no error signals if said measurement time period
ends after said third comparison time interval ends.
2. An apparatus as recited in claim 1 wherein said sonic means
includes means for transmitting the sonic signal toward the datum
in response to a first time reference signal, and includes means
for generating a second time reference signal upon the receipt of
the reflected sonic signal, wherein said first and second time
reference signals respectively define the beginning and end of said
measurement time period.
3. An apparatus as recited in claim 2 wherein said first comparison
time interval begins a delay time period after the receipt of said
first time reference signal, and wherein said delay time period is
selected so that, when the grading implement is positioned at its
nominal position relative to the datum, said measurement time
period is substantially equal to the sum of said delay time period
plus said first comparison time interval plus one half of said
second comparison time interval.
4. An apparatus as recited in claim 3 wherein said apparatus
further includes means for periodically generating said first time
reference signal to periodically initiate a correction of the
position of the grading implement.
5. An apparatus as recited in claim 2 wherein said first comparison
time interval is defined by an output signal of a first monostable
multivibrator triggered by said first time reference signal,
wherein said second comparison time interval is defined by an
output signal of a second monostable multivibrator triggered by the
end of said first comparison time interval, and wherein said third
comparison time interval is defined by an output signal of a third
monostable multivibrator triggered by the end of said second
comparison time interval.
6. An apparatus as recited in claim 5 wherein the durations of said
first, and second, and third comparison time intervals are
respectively determined by timing components coupled to said first,
second, and third monostable multivibrators.
7. An apparatus as recited in claim 5 wherein said comparison means
includes first and second gate means, wherein said first gate means
receives said second time reference signal and the output signal of
said first monostable multivibrator and generates said positive
error signal when both inputs thereto are simultaneously present,
and wherein said second gate means receives said second time
reference signal and the output signal of said third monostable
multivibrator and generates said negative error signal when both
inputs thereto are simultaneously present.
8. An apparatus as recited in claim 1 wherein said first gate means
includes a first AND gate that receives said second time reference
signal and the output signal of said first monostable
multivibrator, and a fourth monostable multivibrator that receives
the output signal of said first AND gate and generates said
positive error signal having a duration defined by timing
components coupled to said fourth monostable multivibrator.
9. An apparatus as recited in claim 7 wherein said second gate
means includes a second AND gate that receives said second time
reference signal and the output signal of said third monostable
multivibrator, and a fifth monostable multivibrator that receives
the output signal of said second AND gate and generates said
negative error signal having a duration defined by timing
components coupled to said fifth monostable multivibrator.
10. An apparatus as recited in claim 1 wherein said first
comparison time interval includes a first subinterval and a second
subinterval with said second subinterval extending between the end
of said first subinterval and the beginning of said second
comparison time interval, said first subinterval defining a large
positive error region and said second subinterval defining a small
positive error region, and wherein said comparison means is further
operable for generating said positive error signal for a longer
duration when said measurement time period ends during said first
subinterval than when said measurement time period ends during said
second subinterval.
11. An apparatus as recited in claim 1 wherein said third
comparison time interval includes a first subinterval and a second
subinterval with said first subinterval extending between the end
of said second comparison time interval and the beginning of said
second subinterval, said first subinterval defining a small
negative error region and said second subinterval defining a large
negative error region, and wherein said comparison means is further
operable for generating said negative error signal for a longer
duration when said measurement time period ends during said second
subinterval than when said measurement time period ends during said
first subinterval.
12. An apparatus for determining the positional error of a grading
implement of an earth-moving machine with respect to a datum, said
apparatus comprising:
means for periodically generating a trigger signal;
ultrasonic means coupled for movement with the implement for
transmitting an ultrasonic signal toward the datum in response to
said trigger signal and for generating an echo signal upon receipt
of an ultrasonic signal reflected from the datum;
timing means for defining a delay time period upon receipt of said
trigger signal and for defining consecutive first, second, and
third comparison time intervals immediately after said delay time
period, wherein said first comparison time interval defines a
positive error region, said second comparison time interval defines
a nominal error region within which the positional error of the
implement is acceptably small, said third comparison time interval
defines a negative error region, and wherein said delay time period
is selected so that the time period between the generation of said
trigger signal and the generation of said echo signal is
substantially equal to the sum of said delay time period plus said
first comparison time interval plus one half of said second
comparison time interval when the grading implement is positioned
at its nominal position relative to the datum; and
comparison means for comparing said echo signal to said comparison
time intervals, for generating a positive error signal if said echo
signal is received during said first comparison time interval, for
generating a negative error signal if said echo signal is received
during said third comparison time interval, and for generating no
error signals if said echo signal is received before said first
comparison time interval begins, if received during said second
comparison time interval, and if received after said third
comparison time interval ends.
13. An apparatus as reoited in claim 12 Wherein said first
comparison time interval consists of a first subinterval that
defines a large positive error region and a second subinterval that
defines a small positive error region, wherein said third
comparison time interval consists of a third subinterval that
defines a small negative error region and a fourth subintnerval
that defines a large negative erorr region, wherein said first
subinterval, said second subinterval, said second comparison time
interval, said third subinterval, and said fourth subinterval occur
in succession, wherein said positive error signal has a shorter
duration if said echo signal is received during said second
subinterval than if said echo signal is recieved during said first
subinterval, and wherein said negative error signal has a shorter
duration if said echo signal is received during said third
subinterval than if said echo signal is received during said fourth
subinterval.
14. An apparatus for controlling the vertical position of a grading
implement of an earth-moving vehicle relative to a datum that
extends alog the direction of travel of the vehicle, wherein said
vehicle includes means coupled to the implement for moving the
implement upward in response to a low error signal and for moving
the implement downward in response to a high error signal, said
apparatus comprising:
sonic means, coupled for movement with the implement and positioned
above the datum, for periodically transmitting a sonic signal
downward toward the datum and for receiving a sonic signal
reflected upward from the datum, wherein the time period between
the transmission and receipt of said sonic signal defines a
measurement time period that is proportional to the separation
distance between said sonic means and the datum;
timing means for periodically defining consecutive first, second,
and third comparison time intervals of finite duration, wherein
said first comparison time interval defines a low error region
beginning at a time after the transmission of the sonic signal by
said sonic means, said second comparison time interval defines a
nominal error region beginning at the end of said first comparison
time interval, and said third comparison time interval defines a
high error region beginning at the end of said second comparison
time interval; and
comparison means for periodically comparing said measurement time
period to said comparison time intervals, for generating said low
error signal if said measurement time period ends during said first
comparison time interval, for generating said high error signal is
said measurement time period ends during said third comparison time
interval, for generating no error signals if said measurement time
period ends during said second comparison time interval, for
generating no error signals if said measurement time period ends
before said first comparison time interval begins, and for
generating no error signals if said measurement time period ends
after said third comparison time interval ends.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to road-construction and
earth-moving vehicles, and relates more particularly to a
non-contacting range sensing and control device for controlling the
position of a grading implement relative to a datum.
2. Description of the Relevant Art
Motor graders, bulldozers, pavers and other road-construction and
earth-moving vehicles are often called upon to produce a graded
surface that follows a predefined datum. In areas of new
construction, for example, the datum might be defined by a string
line supported by stakes placed adjacent to the path to be graded.
In areas of reconstruction, the datum might be defined by a
preexisting curb or pavement surface.
Various devices have been used on earth-moving vehicles to position
the grading implements to obtain the desired graded surfaces. The
grading implements of these vehicles are usually positioned by
hydraulic cylinders that are coupled to mechanisms that support the
grading implements. A typical positioning device includes a datum
sensing device that is mounted on the grading implement and that
senses the position of the datum relative to the implement, and a
control device that signals the hydraulic cylinders to reposition
the implement accordingly.
One such datum sensing device is a string follower, used where the
datum is defined by a string line that is suspended a constant
distance above the desired graded surface. A sensor unit is
attached to the side of the grading implement nearest the string
line, and a pivotable wand extends from the sensor unit and touches
the string line. The sensor is responsive to the rotational
position of the wand as an indication of the position of the
implement relative to the string datum. The wand is often spring
loaded against the string line to ensure contact. One drawback to
the use of a string follower is that if the spring force is
excessive, or if the string line is loosely strung, then the spring
force of the wand can displace the string line from its intended
position and thereby introduce grading errors. Another drawback is
that the operator must stop grading and get out of the cab in order
set the wand onto the string line. Another drawback is that if the
wand falls off of the string line, then the sensor indicates a
large positional error and tries to correct the position of the
implement accordingly, thus causing gouges or other discontinuities
in the graded surface. Still another drawback is that the wand
mechanism typically has limited adjustability, which restricts the
location of the string line relative to the desired surface.
Other datum sensing devices include wheels and skids, which are
useful where the datum is defined by a pre-existing curb or
previously graded surface. A sensor unit is usually mounted to the
side or rear of the grading implement, and a projecting arm pivots
downward to place the wheel or skid on the datum surface. The
sensor unit responds to the rotational position of the arm as a
measure of the position of the implement relative to the datum
surface. One major drawback to the use of wheels and skids is that
they are typically designed for forward movement of the vehicle, so
that in order to allow the vehicle to back up, the wheel or skid
must be lifted up. If the vehicle backs up without lifting such a
wheel or skid, then the mounting mechanism may bend or break
off.
SUMMARY OF THE INVENTION
In accordance with the illustrated preferred embodiment, the
present invention provides a non-embodiment, contacting range
sensing and control device for controlling the position of a
grading implement relative to a datum. More specifically, the range
sensing and control device determines the positional error of the
implement relative to the datum, where the implement is coupled to
a vehicle that moves in a direction substantially parallel to the
datum. The range sensing and control device includes a
non-contacting distance measuring device, a reference circuit, and
a comparison circuit. The distance measuring device is coupled for
movement with the implement, and periodically measures the
separation distance between the distance measuring device and the
datum without contacting the datum. The reference circuit defines
consecutive first, second, and third comparison intervals for
comparison to the measured separation distance, where the first
comparison interval defines a positive error region within which
the positional error of the implement is directed in one direction,
the second comparison interval defines a nominal error region
within which the positional error of the implement is acceptably
small, and the third comparison interval defines a negative error
region within which the positional error of the implement is
directed in an opposite direction. The comparison circuit
periodically compares the separation distance as measured by the
distance measuring device to the comparison intervals as defined by
the reference circuit. In addition, the comparison circuit
generates a positive error signal if the separation distance is
within the limits of the first comparison interval, generates no
error signal if the separation distance is within the limits of the
second comparison interval, and generates a negative error signal
if the separation distance is within the limits of the third
comparison interval.
In the preferred embodiment, the measured separation distance and
the comparison intervals are defined in terms of time. The distance
measuring device is preferably an ultrasonic range finder that can
sense string lines as well as surfaces such as curbs and pavement.
The ultrasonic rangefinder periodically sends out an ultrasonic
pulse and listens for a pulse reflected from the datum. The time
period between the transmission of the initial pulse and the
receipt of the reflected pulse is proportional to the separation
distance between the rangefinder and the datum.
The comparison intervals are also preferably defined in terms of
time. The comparison intervals are preferably consecutive time
intervals that begin subsequent to a delay time period after the
transmission of the ultrasonic pulse. The duration of the delay
time period is adjustable, and is chosen so that the reflected
pulse will be received during the second comparison time interval
when the implement is correctly positioned with respect to the
datum. If the reflected pulse is received earlier, during the first
comparison time interval, then the separation distance is too
small. If the reflected pulse is received later, during the third
comparison time interval, then the separation distance is too
large. In order to decide whether to issue an error signal, and, if
so, to decide the direction or sense of the error, the comparison
circuit must first decide within which comparison time interval the
reflected pulse is received, and must then issue an appropriate
error signal.
The range sensing and control device of the present invention is
responsive only to errors within a correctable range, as defined by
the duration of the comparison time intervals. If the reflected
pulse is received before the start of the first comparison time
interval or after the end of the third comparison time interval,
then the separation distance is deemed too great to correct and no
error signal is generated.
In the preferred embodiment disclosed below, the first and third
comparison time intervals are each subdivided into two
subintervals. The first subinterval at the beginning of the first
comparison time interval and the fourth subinterval at the end of
the third comparison time interval define large error regions,
while the second subinterval at the end of the first comparison
time interval and the third subinterval at the beginning of the
second comparison time interval define small error regions. The
duration of the error signal generated by the comparison circuit is
longer if the reflected pulse is received during a large error
subinterval than if it is received during a small error
subinterval.
There are many advantageous features of the range sensing and
control device of the present invention. First is its ability to
follow a wide range of datums, including string lines, curbing, and
pregraded surfaces. Second is the ease with which the nominal
position of the grading implement can be adjusted by the vehicle
operator. Third is that the device does not contact the datum, so
that string lines can be followed without distortion. Fourth is
that the device does not restrict the maneuverability of the
vehicle. Fifth is the absence of mechanisms that could otherwise
jam. Sixth is the insensitivity to losing track of a string line,
since no error signals are generated if the sensed datum position
is not within the correctable range. Seventh is the ease with which
the operator can engage and disengage the device.
The features and advantages described in the specification are not
all inclusive, and particularly, many additional features and
advantages will be apparent to one of ordinary skill in the art in
view of the drawings, specification and claims hereof. Moreover, it
should be noted that the language used in the specification has
been principally selected for readability and instructional
purposes, and may not have been selected to delineate or
circumscribe the inventive subject matter. In particular, the term
earth-moving vehicle is intended to include motor graders,
bulldozers, pavers, and other such vehicles that carry grading
implements. The term grading implement is intended to include
blades, scrapers, and other implements required to be positioned
relative to a datum. The term sonic includes frequencies in the
ultrasonic range as well as frequencies within the range of human
hearing. The terms positive and negative are relative directional
terms, and do not necessarily refer to a particular direction.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a portion of a motor grader
following a string line datum and having two range sensing and
control devices installed thereon.
FIG. 2 is a block diagram of a range sensing and control device
according to the present invention.
FIG. 3 is a schematic diagram of a portion of the range sensing and
control device of FIG. 2.
FIG. 4 is a timing diagram of a portion of the range sensing and
control device of FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 through 4 of the drawings depict various preferred
embodiments of the present invention for purposes of illustration
only. One skilled in the art will readily recognize from the
following discussion that alternative embodiments of the structures
and methods illustrated herein may be employed without departing
from the principles of the invention described herein.
The preferred embodiment of the present invention is a
non-contacting range sensing and control device for controlling the
position of a grading implement relative to a datum. While the
present invention is directed to a range sensing and control device
that is useful in many applications, the range sensing and control
device is particularly suited for controlling the vertical position
of a blade of a motor grader. Accordingly, the present invention
will be described for purposes of full disclosure as well as
purposes of illustration as practiced with a motor grader.
A motor grader 10 is illustrated in FIG. 1 with the front portion
of the motor grader removed for clarity. Slung underneath the motor
grader 10 is a blade 12, which is mounted on a platform 14 that is
pivotably attached to the front of the motor grader (not shown).
The vertical position of the platform 14 and the blade 12 is
adjusted by two hydraulic cylinders 16. In operation of the motor
grader 10 without the assistance of the range sensing and control
device of the present invention, the operator 18 manually adjusts
the vertical position of the blade 12 through hydraulic controls
coupled to the cylinders 16. The slope of the blade 12 with respect
to horizontal can be varied by independent movement of the
cylinders 16. Additional hydraulic systems (not shown) are operable
for rotating the blade 12 around a vertical axis, varying the angle
of attack of the blade, and moving the blade laterally. Forward
motion of the motor grader 10 evenly spreads a pile of dirt or
gravel 20 into a graded surface 22.
Two sensor units 24 of the present invention are shown mounted on
frames 26 to both sides of the blade 12. Both sensor units 24
overhang the outer edges of the blade 12 and are positioned above a
datum, such as a string line 28, that is located just outside of
the width of the blade and that extends along the direction of
travel of the motor grader 10. Each sensor unit is connected via an
electrical cable 30 to a control box (not shown) located near the
operator 18 in the operator's cab. Either of the two sensor units
24 can be used to sense a datum 28 for controlling the vertical
position of the blade 12. Alternatively, the sensor units 24 could
sense two separate datums, one on each side of the motor grader 10,
for controlling both the vertical position and the slope of the
blade 12.
The circuitry of the range sensing and control device of the
present invention is divided between the sensor unit 24 suspended
over the datum and the control box located in the cab. In reference
to FIG. 2, one component of the range sensing and control device 32
that is contained in the sensor unit 24 is an ultrasonic
transmitter/receiver or rangefinder 34. An oscillator 36
periodically supplies a trigger signal to the rangefinder 34, which
in response transmits an ultrasonic signal downward toward the
datum 28. A portion of that ultrasonic signal is reflected back
from the datum 28 to the rangefinder 34, which the rangefinder
responds to by generating an echo signal. The rangefinder 34
responds only to the first received reflected signal; subsequently
received signals, such as might be reflected by the ground under a
string line, are ignored.
The time period between the generation of the trigger signal and
the generation of the echo signal is a measure of the separation
distance between the rangefinder 34 and the datum 28. Since the
rangefinder 34 is fixedly attached to and moveable with the blade
12, the rangefinder provides means for measuring the position of
the blade 12 relative to the datum 28. Of course, the datum need
not be a string line because the rangefinder will sense a broad
range of surfaces such as curbs, pavement, and previously graded
surfaces. Preferably, the rangefinder 34 includes an SN28827
ranging module manufactured by Texas Instruments, and a #8667
electrostatic transducer manufactured by Polaroid.
The trigger signal generated by the oscillator 36 and the echo
signal generated by the rangefinder 34 are supplied to a window
detector circuit 38. The window detector circuit 38 includes two
functional elements, a timing circuit and a comparison circuit. The
timing circuit defines a measurement window that begins after a
time delay, as specified by a window position adjustment circuit
40, subsequent to the receipt by the timing circuit of the trigger
signal. The measurement window consists of three consecutive time
intervals, the first of which defines a positive error region, the
second of which defines a nominal error region, and the third of
which defines a negative error region.
The comparison circuit determines within which interval of the
measurement window that the echo signal arrives, and issues an
appropriate error signal. If the echo signal arrives during the
second timing interval, the blade is at or near its desired
position, and no error signal is issued. If the echo signal arrives
during the first timing interval, which means that the separation
distance between the sensor unit 24 and the datum 28 is less than
desired, then the blade is too low and an error signal of one sense
is generated. If the echo signal arrives during the third timing
interval, which means that the separation distance between the
sensor unit 24 and the datum 28 is greater than desired, then the
blade is too high and an error signal of an opposite sense is
generated.
The error signals generated by the comparison circuit are routed
through a debounce circuit 42, which acts as a filter to prevent
false triggering, to a valve driver 44. The valve driver 44
controls a hydraulic valve 46 that supplies hydraulic pressure to
one side or the other of the hydraulic cylinders 16, depending upon
whether the blade is to raised or lowered. A switch 48, connected
to the valve driver 44 and preferably located in the control box
near the operator, allows the range sensing and control device 32
to be disconnected and the blade control to be accomplished
manually.
The details of the circuitry of the oscillator 36, the window
position adjustment circuit 40, and the window detector 38 will now
be described with the aid of FIGS. 3 and 4. The oscillator 36 is
preferably a model 555 monolithic timing circuit 50, with the
ground pin (1) connected to ground, and the power pin (8) and the
reset pin (4) connected to a source of positive voltage, V+. The
timer 50 is wired for astable operation, with a capacitor 52
coupled between the commonly connected trigger and threshold pins
(2 and 6) and ground, a resistor 54 coupled between the threshold
pin (6) and the discharge pin (7), and a resistor 56 coupled
between the discharge pin (7) and V+. The output pin (3) supplies
the trigger signal to the rangefinder 34 and to the window detector
38.
As so wired, the timer 50 retriggers itself, and causes the voltage
on the capacitor 52 to oscillate between one third of V+ and two
thirds of V+. The capacitor 52 charges through resistors 54 and 56
to two thirds of V+, and discharges through resistor 54 to one
third of V+. Since the value of resistor 56 is much larger than
that of resistor 54, the resulting waveform of the trigger signal
is an inverted pulse, as shown in FIG. 4. Preferably, the frequency
of the trigger signal is about five cycles per second. As applied
to the rangefinder 34, the trigger signal serves as both a trigger
signal, which initiates the generation of the ultrasonic pulse, and
an enable signal, which enables the rangefinder circuitry to
generate the echo signal in response to the received ultrasonic
pulse reflected from the datum 28.
Within the window detector circuit 38 is the timing and comparison
circuitry. The trigger signal from the timer 50 is applied to the
rising edge trigger input pin of a delay monostable multivibrator
58, which generates the window adjust signal. The window adjust
signal (FIG. 4) is initially logic low, is set logic high by the
rising edge of the trigger signal, and is reset low after a delay
time period 60. The duration of the delay time period 60 is
determined by the RC product of a capacitor 62 connected between
timing pins T1 and T2, and series resistors 64 and 66 connected
between pin T2 and V+. Resistor 66, which comprises the window
position adjustment circuit 40, is adjustable so that the duration
of the delay time period 60 can be adjusted to vary the nominal
position of the blade 12 relative to the datum 28.
The window adjust signal generated by the delay multivibrator 58 is
supplied to a series of five timing monostable multivibrators 68,
70, 72, 74, and 76. The timing multivibrators are cascaded
together, with the output of each timing multivibrator coupled to
the input of the next timing multivibrator in line. The five timing
multivibrators define the comparison time intervals that comprise
the measurement window. Timing multivibrator 68 receives the window
adjust signal from the delay multivibrator 58 at its falling edge
trigger input pin, and generates a low coarse interval signal (FIG.
4). The high pulse 78 of the low coarse interval signal begins at
the falling edge of the window adjust signal, that is, after the
delay time period fixed by the delay multivibrator 58. The duration
of the high pulse 78 of the low coarse interval signal is
determined by the values of capacitor 80 and resistor 82, which are
connected to the timing pins T1 and T2 of the timing multivibrator
68.
Timing multivibrator 70 receives the low coarse interval signal
from the timing multivibrator 68 at its falling edge trigger input
pin, and generates a low fine interval signal (FIG. 4). The high
pulse 84 of the low fine interval signal begins at the falling edge
of the low coarse interval signal. The duration of the high pulse
84 of the low fine interval signal is determined by the values of
capacitor 86 and resistor 88, which are connected to the timing
pins T1 and T2 of the timing multivibrator 70.
Timing multivibrator 72 receives the low fine interval signal from
the timing multivibrator 70 at its falling edge trigger input pin,
and generates an on grade interval signal (FIG. 4). The high pulse
90 of the on grade interval signal begins at the falling edge of
the low fine interval signal. The duration of the high pulse 90 of
the on grade interval signal is determined by the values of
capacitor 92 and resistor 94, which are connected to the timing
pins T1 and T2 of the timing multivibrator 72.
Timing multivibrator 74 receives the on grade interval signal from
the timing multivibrator 72 at its falling edge trigger input pin,
and generates a high fine interval signal (FIG. 4). The high pulse
96 of the high fine interval signal begins at the falling edge of
the on grade interval signal. The duration of the high pulse 96 of
the high fine interval signal is determined by the values of
capacitor 98 and resistor 100, which are connected to the timing
pins T1 and T2 of the timing multivibrator 74.
Timing multivibrator 76 receives the high fine interval signal from
the timing multivibrator 74 at its falling edge trigger input pin,
and generates a high coarse interval signal (FIG. 4). The high
pulse 102 of the high coarse interval signal begins at the falling
edge of the high fine interval signal. The duration of the high
pulse 102 of the high coarse interval signal is determined by the
values of capacitor 104 and resistor 106, which are connected to
the timing pins T1 and T2 of the timing multivibrator 76.
Together, the five consecutive interval pulses 78, 84, 90, 96, and
102 define the duration of the measurement time period or window
108. Using terms introduced above in the Summary of the Invention,
the high pulses of the low coarse interval signal and the low fine
interval signal together define the first comparison time interval,
with the high pulse of the low coarse interval signal defining the
first subinterval and the high pulse of the low fine interval
signal defining the second subinterval. The high pulse of the on
grade interval signal defines the second comparison time interval.
Also, the high pulses of the high fine interval signal and the high
coarse interval signal together define the third comparison time
interval, with the high pulse of the high fine interval signal
defining the third subinterval and the high pulse of the high
coarse interval signal defining the fourth subinterval.
The monostable multivibrators are preferably model 4538's, and the
positive voltage V+ is preferably about six volts. With the
components of the timing circuit having the values as specified in
FIG. 3, the approximate durations of the intervals are:
______________________________________ duration length in
milliseconds in inches ______________________________________ low
coarse interval 0.18 1.2 low fine interval 0.18 1.2 on grade
interval 0.022 0.30 high fine interval 0.18 1.2 high coarse
interval 0.18 1.2 ______________________________________
Thus, the total measurement window is about 0.74 milliseconds or
5.1 inches in width, with the positive error region comprising
about 0.36 milliseconds and 2.4 inches, the nominal error region
comprising about 0.022 milliseconds and 0.30 inches, and the
negative error region comprising about 0.36 milliseconds and 2.4
inches.
Having thus described the timing circuit portion of the window
detector 38, the comparison circuit portion will now be described.
The output pins of each of the timing multivibrators 68, 70, 72,
74, and 76 are coupled through diode AND gates 110, 112, 114, 116,
and 118, respectively, to the falling edge trigger input pins of
signaling monostable multivibrators 120, 122, 124, 126, and 128.
Each AND gate consists of two diodes 125 and 127, and a resistor
129. The anodes of the diodes 125 and 127 are connected to an
output node 131, which is connected through resistor 129 to V+. The
cathodes of the diodes 125 and 127 serve as the input terminals of
the AND gate. One input terminal of each AND gate is connected to
the output terminal of a timing multivibrator 68, 70, 72, 74, or
76. The other input terminal is coupled to receive an echo pulse
signal generated by a monostable multivibrator 130.
The multivibrator 130 receives the echo signal from the rangefinder
34 at its rising edge trigger input pin. The duration of the
positive pulse of the echo pulse signal is preferably much shorter
than the duration of the timing intervals pulses 78, 84, 90, 96,
and 102, and is determined by the values of capacitor 132 and
resistor 134, which are connected to the timing pins T1 and T2 of
the multivibrator 130.
The AND gates 110, 112, 114, 116, and 118 logically AND the echo
pulse signal with each of the five timing interval signals. If both
the echo pulse signal and one of the timing interval signals are
simultaneously positive, then the corresponding signaling
multivibrator will be triggered. Once triggered, the signaling
multivibrator issues a pulsed output, the duration of which is
determined by a capacitor and resistor connected to its timing
pins.
Signaling multivibrators 120 and 122, which correspond to the low
coarse and low fine intervals, generate error signals that are
supplied to the valve driver 44. The error signals reflect a
positional error of the blade 12 in one direction, namely that the
blade is too low. In response to either of the two error signals,
the valve driver 44 causes the blade 12 to be raised by opening the
valve 46 to the appropriate side of the hydraulic cylinders 16 for
the duration of the error signal pulse. If the error signal is
generated by the low coarse multivibrator 120, which indicates a
relatively large positional error, the duration of the positive
pulse is longer than if the error signal is generated by the low
fine multivibrator 122, which indicates a relatively small
positional error. The error signal also causes a light emitting
diode 136 to light for the duration of the pulse.
As a first example, assume that the separation distance between the
rangefinder 34 and the datum 28 is indicated by the time period 138
(FIG. 4) between the rising edge of the trigger signal and the
rising edge of the echo signal. Since the echo pulse and the low
coarse interval signals are simultaneously positive, AND gate 110
triggers the low coarse signaling multivibrator 120, which issues a
long duration error signal to the valve driver to raise the blade
12. The LED 136 lights up to show the operator 18 that a low
reading was obtained and that the blade 12 is being repositioned
upward.
In a second example, assume that the echo pulse occurs during the
second timing interval, wherein the echo pulse and the on grade
interval signals are simultaneously positive (see FIG. 4). The AND
gate 114 triggers the on grade signaling multivibrator 124, which
generates an output signal that lights a light emitting diode 140
that indicates an on grade reading. Since no correction of the
blade 12 is required in this case, no error signal is supplied to
the valve driver 44.
Signaling multivibrators 126 and 128, which correspond to the high
fine and high coarse intervals, generate error signals that are
supplied to the valve driver 44. The error signals reflect a
positional error of the blade 12 in an opposite direction, namely
that the blade is too high. In response to either of the two error
signals, the valve driver 44 causes the blade 12 to be lowered by
opening the valve 46 to the appropriate side of the hydraulic
cylinders 16 for the duration of the error signal pulse. If the
error signal is generated by the high coarse multivibrator 128,
which indicates a relatively large positional error, the duration
of the positive pulse is longer than if the error signal is
generated by the high fine multivibrator 126, which indicates a
relatively small positional error. The error signal also causes a
light emitting diode 142 to light for the duration of the
pulse.
As a third example, as shown in FIG. 4, assume that the echo pulse
and the high fine interval signals are simultaneously positive. The
AND gate 116 triggers the high fine signaling multivibrator 126 to
issue a short duration error signal to the valve driver 44 to lower
the blade 12. The LED 142 lights up to show the operator 18 that a
high reading was obtained and that the blade 12 is being
repositioned downward.
With the components of the comparison circuit having the values as
specified in FIG. 3, the approximate duration of the error
correction signals is:
______________________________________ duration, milliseconds
______________________________________ Raise large error 200 small
error 68 Lower large error 200 small error 68
______________________________________
Preferably, the LED's 136, 140, and 142 are located in the control
box near the operator 18. Also located in the control box are the
auto/manual switch 48, and the window position adjustment resistor
66.
From the above description, it will be apparent that the invention
disclosed herein provides a non-contacting range sensing and
control device for controlling the position of a grading implement
relative to a datum. The foregoing discussion discloses and
describes merely exemplary methods and embodiments of the present
invention. As will be understood by those familiar with the art,
the invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof.
For example, a sensor unit 24 could be positioned to measure the
lateral distance between the blade 12 and the vertical side of a
curb, with any resulting error signal being used to laterally
reposition the blade. Or, the ultrasonic rangefinder, which defines
the separation distance in terms of a time period, could be
replaced by an optical rangefinder, which would define the
separation distance as a numerical value that could be compared to
numerically defined comparison intervals to generate the
appropriate error signals.
Accordingly, the disclosure of the present invention is intended to
be illustrative, but not limiting, of the scope of the invention,
which is set forth in the following claims.
* * * * *